This invention relates to carbon bonded refractory brick and, more particularly, to such brick having particular utility for lining various metal making furnaces.
Carbon bonded refractory brick have been used for some time in basic oxygen steel making furnaces and electric arc steel making furnaces because such brick have excellent properties of corrosion resistance and resistance to disintegration. Typically, in carbon bonded refractory brick of the prior art, tars and pitches have been used as binders for the refractory aggregates. The binders serve to bond the material, forming the refractory aggregates together during pressing, and to leave a carbon residue during operating life of the furnace incorporating the brick. Typically, the refractory aggregate comprises combinations of carbon bearing material and magnesite.
The use of tars and pitches as binders has certain undesirable consequences both in the manufacturing of the refractory and in its service life. For example, pitch bonded refractories must be produced by heating the batches of the aggregate material since, at room temperature, pitch is a solid. To produce a satisfactory brick, the pitch must be used in a molten state and mixed with the refractory aggregate. Generally, the pitch is placed in a molten state when heated to a temperature between 250.degree. to 400.degree. F. By heating the pitch to place same in a molten state, a substantial amount of fumes is produced. This may have an adverse affect on the health and, due to the nauseous odor, also on the morale of the workers in the plant making the refractory brick. Further, heating the batch of aggregate and pitch utilizes a significant quantity of energy.
When pitch bonded refractories are placed in service, the pitch will again soften when the operating temperature of the furnace falls within the temperature range of 200.degree. to 600.degree. F. During the burn-in and early heating of a newly lined furnace, as for example in the cone of a basic oxygen furnace, the brick could be subject to fragmental breaking or spalling due to the softening of the pitch.
To avoid the health and operating problems associated with the utilization of pitch or tar as a binder, resin substitutes for the pitch and tar have been sought. The suitable resins which have been utilized include phenolformaldehyde type (novolaks and resols), furan type, and lignin modified phenolics to name a few. Heretofore, the major disadvantage of using resin binders instead of tars and pitches in the production of carbon bonded refractories has been the cost of the resin. Also, the density and porosity of the resin bonded brick after coking has not been of the same quality as tar bonded brick. Further, many liquid resins which have been used have been fairly viscous materials which require slight heating prior to production of the brick.